import * as qs from "querystring";
import { parse } from "url";
import * as base64id from "base64id";
import transports from "./transports";
import { EventEmitter } from "events";
import { Socket } from "./socket";
import debugModule from "debug";
import { serialize } from "cookie";
import { Server as DEFAULT_WS_ENGINE } from "ws";
import { IncomingMessage, Server as HttpServer } from "http";
import { CookieSerializeOptions } from "cookie";
import { CorsOptions } from "cors";

const debug = debugModule("engine");

type Transport = "polling" | "websocket";

export interface AttachOptions {
  /**
   * name of the path to capture
   * @default "/engine.io"
   */
  path?: string;
  /**
   * destroy unhandled upgrade requests
   * @default true
   */
  destroyUpgrade?: boolean;
  /**
   * milliseconds after which unhandled requests are ended
   * @default 1000
   */
  destroyUpgradeTimeout?: number;
}

export interface ServerOptions {
  /**
   * how many ms without a pong packet to consider the connection closed
   * @default 20000
   */
  pingTimeout?: number;
  /**
   * how many ms before sending a new ping packet
   * @default 25000
   */
  pingInterval?: number;
  /**
   * how many ms before an uncompleted transport upgrade is cancelled
   * @default 10000
   */
  upgradeTimeout?: number;
  /**
   * how many bytes or characters a message can be, before closing the session (to avoid DoS).
   * @default 1e5 (100 KB)
   */
  maxHttpBufferSize?: number;
  /**
   * A function that receives a given handshake or upgrade request as its first parameter,
   * and can decide whether to continue or not. The second argument is a function that needs
   * to be called with the decided information: fn(err, success), where success is a boolean
   * value where false means that the request is rejected, and err is an error code.
   */
  allowRequest?: (
    req: IncomingMessage,
    fn: (err: string | null | undefined, success: boolean) => void
  ) => void;
  /**
   * the low-level transports that are enabled
   * @default ["polling", "websocket"]
   */
  transports?: Transport[];
  /**
   * whether to allow transport upgrades
   * @default true
   */
  allowUpgrades?: boolean;
  /**
   * parameters of the WebSocket permessage-deflate extension (see ws module api docs). Set to false to disable.
   * @default false
   */
  perMessageDeflate?: boolean | object;
  /**
   * parameters of the http compression for the polling transports (see zlib api docs). Set to false to disable.
   * @default true
   */
  httpCompression?: boolean | object;
  /**
   * what WebSocket server implementation to use. Specified module must
   * conform to the ws interface (see ws module api docs).
   * An alternative c++ addon is also available by installing eiows module.
   *
   * @default `require("ws").Server`
   */
  wsEngine?: any;
  /**
   * an optional packet which will be concatenated to the handshake packet emitted by Engine.IO.
   */
  initialPacket?: any;
  /**
   * configuration of the cookie that contains the client sid to send as part of handshake response headers. This cookie
   * might be used for sticky-session. Defaults to not sending any cookie.
   * @default false
   */
  cookie?: (CookieSerializeOptions & { name: string }) | boolean;
  /**
   * the options that will be forwarded to the cors module
   */
  cors?: CorsOptions;
  /**
   * whether to enable compatibility with Socket.IO v2 clients
   * @default false
   */
  allowEIO3?: boolean;
}

export abstract class BaseServer extends EventEmitter {
  public opts: ServerOptions;

  protected clients: any;
  private clientsCount: number;
  protected corsMiddleware: Function;

  /**
   * Server constructor.
   *
   * @param {Object} opts - options
   * @api public
   */
  constructor(opts: ServerOptions = {}) {
    super();

    this.clients = {};
    this.clientsCount = 0;

    this.opts = Object.assign(
      {
        wsEngine: DEFAULT_WS_ENGINE,
        pingTimeout: 20000,
        pingInterval: 25000,
        upgradeTimeout: 10000,
        maxHttpBufferSize: 1e6,
        transports: Object.keys(transports),
        allowUpgrades: true,
        httpCompression: {
          threshold: 1024
        },
        cors: false,
        allowEIO3: false
      },
      opts
    );

    if (opts.cookie) {
      this.opts.cookie = Object.assign(
        {
          name: "io",
          path: "/",
          // @ts-ignore
          httpOnly: opts.cookie.path !== false,
          sameSite: "lax"
        },
        opts.cookie
      );
    }

    if (this.opts.cors) {
      this.corsMiddleware = require("cors")(this.opts.cors);
    }

    if (opts.perMessageDeflate) {
      this.opts.perMessageDeflate = Object.assign(
        {
          threshold: 1024
        },
        opts.perMessageDeflate
      );
    }

    this.init();
  }

  protected abstract init();

  /**
   * Returns a list of available transports for upgrade given a certain transport.
   *
   * @return {Array}
   * @api public
   */
  public upgrades(transport) {
    if (!this.opts.allowUpgrades) return [];
    return transports[transport].upgradesTo || [];
  }

  /**
   * Verifies a request.
   *
   * @param {http.IncomingMessage}
   * @return {Boolean} whether the request is valid
   * @api private
   */
  protected verify(req, upgrade, fn) {
    // transport check
    const transport = req._query.transport;
    if (!~this.opts.transports.indexOf(transport)) {
      debug('unknown transport "%s"', transport);
      return fn(Server.errors.UNKNOWN_TRANSPORT, { transport });
    }

    // 'Origin' header check
    const isOriginInvalid = checkInvalidHeaderChar(req.headers.origin);
    if (isOriginInvalid) {
      const origin = req.headers.origin;
      req.headers.origin = null;
      debug("origin header invalid");
      return fn(Server.errors.BAD_REQUEST, {
        name: "INVALID_ORIGIN",
        origin
      });
    }

    // sid check
    const sid = req._query.sid;
    if (sid) {
      if (!this.clients.hasOwnProperty(sid)) {
        debug('unknown sid "%s"', sid);
        return fn(Server.errors.UNKNOWN_SID, {
          sid
        });
      }
      const previousTransport = this.clients[sid].transport.name;
      if (!upgrade && previousTransport !== transport) {
        debug("bad request: unexpected transport without upgrade");
        return fn(Server.errors.BAD_REQUEST, {
          name: "TRANSPORT_MISMATCH",
          transport,
          previousTransport
        });
      }
    } else {
      // handshake is GET only
      if ("GET" !== req.method) {
        return fn(Server.errors.BAD_HANDSHAKE_METHOD, {
          method: req.method
        });
      }

      if (!this.opts.allowRequest) return fn();

      return this.opts.allowRequest(req, (message, success) => {
        if (!success) {
          return fn(Server.errors.FORBIDDEN, {
            message
          });
        }
        fn();
      });
    }

    fn();
  }

  /**
   * Closes all clients.
   *
   * @api public
   */
  public close() {
    debug("closing all open clients");
    for (let i in this.clients) {
      if (this.clients.hasOwnProperty(i)) {
        this.clients[i].close(true);
      }
    }
    this.cleanup();
    return this;
  }

  protected abstract cleanup();

  /**
   * generate a socket id.
   * Overwrite this method to generate your custom socket id
   *
   * @param {Object} request object
   * @api public
   */
  public generateId(req) {
    return base64id.generateId();
  }

  /**
   * Handshakes a new client.
   *
   * @param {String} transport name
   * @param {Object} request object
   * @param {Function} closeConnection
   *
   * @api protected
   */
  protected async handshake(transportName, req, closeConnection) {
    const protocol = req._query.EIO === "4" ? 4 : 3; // 3rd revision by default
    if (protocol === 3 && !this.opts.allowEIO3) {
      debug("unsupported protocol version");
      this.emit("connection_error", {
        req,
        code: Server.errors.UNSUPPORTED_PROTOCOL_VERSION,
        message:
          Server.errorMessages[Server.errors.UNSUPPORTED_PROTOCOL_VERSION],
        context: {
          protocol
        }
      });
      closeConnection(Server.errors.UNSUPPORTED_PROTOCOL_VERSION);
      return;
    }

    let id;
    try {
      id = await this.generateId(req);
    } catch (e) {
      debug("error while generating an id");
      this.emit("connection_error", {
        req,
        code: Server.errors.BAD_REQUEST,
        message: Server.errorMessages[Server.errors.BAD_REQUEST],
        context: {
          name: "ID_GENERATION_ERROR",
          error: e
        }
      });
      closeConnection(Server.errors.BAD_REQUEST);
      return;
    }

    debug('handshaking client "%s"', id);

    try {
      var transport = this.createTransport(transportName, req);
      if ("polling" === transportName) {
        transport.maxHttpBufferSize = this.opts.maxHttpBufferSize;
        transport.httpCompression = this.opts.httpCompression;
      } else if ("websocket" === transportName) {
        transport.perMessageDeflate = this.opts.perMessageDeflate;
      }

      if (req._query && req._query.b64) {
        transport.supportsBinary = false;
      } else {
        transport.supportsBinary = true;
      }
    } catch (e) {
      debug('error handshaking to transport "%s"', transportName);
      this.emit("connection_error", {
        req,
        code: Server.errors.BAD_REQUEST,
        message: Server.errorMessages[Server.errors.BAD_REQUEST],
        context: {
          name: "TRANSPORT_HANDSHAKE_ERROR",
          error: e
        }
      });
      closeConnection(Server.errors.BAD_REQUEST);
      return;
    }
    const socket = new Socket(id, this, transport, req, protocol);

    transport.on("headers", (headers, req) => {
      const isInitialRequest = !req._query.sid;

      if (isInitialRequest) {
        if (this.opts.cookie) {
          headers["Set-Cookie"] = [
            // @ts-ignore
            serialize(this.opts.cookie.name, id, this.opts.cookie)
          ];
        }
        this.emit("initial_headers", headers, req);
      }
      this.emit("headers", headers, req);
    });

    transport.onRequest(req);

    this.clients[id] = socket;
    this.clientsCount++;

    socket.once("close", () => {
      delete this.clients[id];
      this.clientsCount--;
    });

    this.emit("connection", socket);

    return transport;
  }

  protected abstract createTransport(transportName, req);

  /**
   * Protocol errors mappings.
   */

  static errors = {
    UNKNOWN_TRANSPORT: 0,
    UNKNOWN_SID: 1,
    BAD_HANDSHAKE_METHOD: 2,
    BAD_REQUEST: 3,
    FORBIDDEN: 4,
    UNSUPPORTED_PROTOCOL_VERSION: 5
  };

  static errorMessages = {
    0: "Transport unknown",
    1: "Session ID unknown",
    2: "Bad handshake method",
    3: "Bad request",
    4: "Forbidden",
    5: "Unsupported protocol version"
  };
}

export class Server extends BaseServer {
  public httpServer?: HttpServer;
  private ws: any;

  /**
   * Initialize websocket server
   *
   * @api protected
   */
  protected init() {
    if (!~this.opts.transports.indexOf("websocket")) return;

    if (this.ws) this.ws.close();

    this.ws = new this.opts.wsEngine({
      noServer: true,
      clientTracking: false,
      perMessageDeflate: this.opts.perMessageDeflate,
      maxPayload: this.opts.maxHttpBufferSize
    });

    if (typeof this.ws.on === "function") {
      this.ws.on("headers", (headersArray, req) => {
        // note: 'ws' uses an array of headers, while Engine.IO uses an object (response.writeHead() accepts both formats)
        // we could also try to parse the array and then sync the values, but that will be error-prone
        const additionalHeaders = {};

        const isInitialRequest = !req._query.sid;
        if (isInitialRequest) {
          this.emit("initial_headers", additionalHeaders, req);
        }

        this.emit("headers", additionalHeaders, req);

        Object.keys(additionalHeaders).forEach(key => {
          headersArray.push(`${key}: ${additionalHeaders[key]}`);
        });
      });
    }
  }

  protected cleanup() {
    if (this.ws) {
      debug("closing webSocketServer");
      this.ws.close();
      // don't delete this.ws because it can be used again if the http server starts listening again
    }
  }

  /**
   * Prepares a request by processing the query string.
   *
   * @api private
   */
  private prepare(req) {
    // try to leverage pre-existing `req._query` (e.g: from connect)
    if (!req._query) {
      req._query = ~req.url.indexOf("?") ? qs.parse(parse(req.url).query) : {};
    }
  }

  protected createTransport(transportName, req) {
    return new transports[transportName](req);
  }

  /**
   * Handles an Engine.IO HTTP request.
   *
   * @param {http.IncomingMessage} request
   * @param {http.ServerResponse|http.OutgoingMessage} response
   * @api public
   */
  public handleRequest(req, res) {
    debug('handling "%s" http request "%s"', req.method, req.url);
    this.prepare(req);
    req.res = res;

    const callback = (errorCode, errorContext) => {
      if (errorCode !== undefined) {
        this.emit("connection_error", {
          req,
          code: errorCode,
          message: Server.errorMessages[errorCode],
          context: errorContext
        });
        abortRequest(res, errorCode, errorContext);
        return;
      }

      if (req._query.sid) {
        debug("setting new request for existing client");
        this.clients[req._query.sid].transport.onRequest(req);
      } else {
        const closeConnection = (errorCode, errorContext) =>
          abortRequest(res, errorCode, errorContext);
        this.handshake(req._query.transport, req, closeConnection);
      }
    };

    if (this.corsMiddleware) {
      this.corsMiddleware.call(null, req, res, () => {
        this.verify(req, false, callback);
      });
    } else {
      this.verify(req, false, callback);
    }
  }

  /**
   * Handles an Engine.IO HTTP Upgrade.
   *
   * @api public
   */
  public handleUpgrade(req, socket, upgradeHead) {
    this.prepare(req);

    this.verify(req, true, (errorCode, errorContext) => {
      if (errorCode) {
        this.emit("connection_error", {
          req,
          code: errorCode,
          message: Server.errorMessages[errorCode],
          context: errorContext
        });
        abortUpgrade(socket, errorCode, errorContext);
        return;
      }

      const head = Buffer.from(upgradeHead); // eslint-disable-line node/no-deprecated-api
      upgradeHead = null;

      // delegate to ws
      this.ws.handleUpgrade(req, socket, head, websocket => {
        this.onWebSocket(req, socket, websocket);
      });
    });
  }

  /**
   * Called upon a ws.io connection.
   *
   * @param {ws.Socket} websocket
   * @api private
   */
  private onWebSocket(req, socket, websocket) {
    websocket.on("error", onUpgradeError);

    if (
      transports[req._query.transport] !== undefined &&
      !transports[req._query.transport].prototype.handlesUpgrades
    ) {
      debug("transport doesnt handle upgraded requests");
      websocket.close();
      return;
    }

    // get client id
    const id = req._query.sid;

    // keep a reference to the ws.Socket
    req.websocket = websocket;

    if (id) {
      const client = this.clients[id];
      if (!client) {
        debug("upgrade attempt for closed client");
        websocket.close();
      } else if (client.upgrading) {
        debug("transport has already been trying to upgrade");
        websocket.close();
      } else if (client.upgraded) {
        debug("transport had already been upgraded");
        websocket.close();
      } else {
        debug("upgrading existing transport");

        // transport error handling takes over
        websocket.removeListener("error", onUpgradeError);

        const transport = this.createTransport(req._query.transport, req);
        if (req._query && req._query.b64) {
          transport.supportsBinary = false;
        } else {
          transport.supportsBinary = true;
        }
        transport.perMessageDeflate = this.opts.perMessageDeflate;
        client.maybeUpgrade(transport);
      }
    } else {
      // transport error handling takes over
      websocket.removeListener("error", onUpgradeError);

      const closeConnection = (errorCode, errorContext) =>
        abortUpgrade(socket, errorCode, errorContext);
      this.handshake(req._query.transport, req, closeConnection);
    }

    function onUpgradeError() {
      debug("websocket error before upgrade");
      // websocket.close() not needed
    }
  }

  /**
   * Captures upgrade requests for a http.Server.
   *
   * @param {http.Server} server
   * @param {Object} options
   * @api public
   */
  public attach(server: HttpServer, options: AttachOptions = {}) {
    let path = (options.path || "/engine.io").replace(/\/$/, "");

    const destroyUpgradeTimeout = options.destroyUpgradeTimeout || 1000;

    // normalize path
    path += "/";

    function check(req) {
      return path === req.url.substr(0, path.length);
    }

    // cache and clean up listeners
    const listeners = server.listeners("request").slice(0);
    server.removeAllListeners("request");
    server.on("close", this.close.bind(this));
    server.on("listening", this.init.bind(this));

    // add request handler
    server.on("request", (req, res) => {
      if (check(req)) {
        debug('intercepting request for path "%s"', path);
        this.handleRequest(req, res);
      } else {
        let i = 0;
        const l = listeners.length;
        for (; i < l; i++) {
          listeners[i].call(server, req, res);
        }
      }
    });

    if (~this.opts.transports.indexOf("websocket")) {
      server.on("upgrade", (req, socket, head) => {
        if (check(req)) {
          this.handleUpgrade(req, socket, head);
        } else if (false !== options.destroyUpgrade) {
          // default node behavior is to disconnect when no handlers
          // but by adding a handler, we prevent that
          // and if no eio thing handles the upgrade
          // then the socket needs to die!
          setTimeout(function() {
            // @ts-ignore
            if (socket.writable && socket.bytesWritten <= 0) {
              return socket.end();
            }
          }, destroyUpgradeTimeout);
        }
      });
    }
  }
}

/**
 * Close the HTTP long-polling request
 *
 * @param res - the response object
 * @param errorCode - the error code
 * @param errorContext - additional error context
 *
 * @api private
 */

function abortRequest(res, errorCode, errorContext) {
  const statusCode = errorCode === Server.errors.FORBIDDEN ? 403 : 400;
  const message =
    errorContext && errorContext.message
      ? errorContext.message
      : Server.errorMessages[errorCode];

  res.writeHead(statusCode, { "Content-Type": "application/json" });
  res.end(
    JSON.stringify({
      code: errorCode,
      message
    })
  );
}

/**
 * Close the WebSocket connection
 *
 * @param {net.Socket} socket
 * @param {string} errorCode - the error code
 * @param {object} errorContext - additional error context
 *
 * @api private
 */

function abortUpgrade(
  socket,
  errorCode,
  errorContext: { message?: string } = {}
) {
  socket.on("error", () => {
    debug("ignoring error from closed connection");
  });
  if (socket.writable) {
    const message = errorContext.message || Server.errorMessages[errorCode];
    const length = Buffer.byteLength(message);
    socket.write(
      "HTTP/1.1 400 Bad Request\r\n" +
        "Connection: close\r\n" +
        "Content-type: text/html\r\n" +
        "Content-Length: " +
        length +
        "\r\n" +
        "\r\n" +
        message
    );
  }
  socket.destroy();
}

/* eslint-disable */

/**
 * From https://github.com/nodejs/node/blob/v8.4.0/lib/_http_common.js#L303-L354
 *
 * True if val contains an invalid field-vchar
 *  field-value    = *( field-content / obs-fold )
 *  field-content  = field-vchar [ 1*( SP / HTAB ) field-vchar ]
 *  field-vchar    = VCHAR / obs-text
 *
 * checkInvalidHeaderChar() is currently designed to be inlinable by v8,
 * so take care when making changes to the implementation so that the source
 * code size does not exceed v8's default max_inlined_source_size setting.
 **/
// prettier-ignore
const validHdrChars = [
  0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, // 0 - 15
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 16 - 31
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 32 - 47
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 48 - 63
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 64 - 79
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 80 - 95
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 96 - 111
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, // 112 - 127
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 128 ...
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1  // ... 255
]

function checkInvalidHeaderChar(val) {
  val += "";
  if (val.length < 1) return false;
  if (!validHdrChars[val.charCodeAt(0)]) {
    debug('invalid header, index 0, char "%s"', val.charCodeAt(0));
    return true;
  }
  if (val.length < 2) return false;
  if (!validHdrChars[val.charCodeAt(1)]) {
    debug('invalid header, index 1, char "%s"', val.charCodeAt(1));
    return true;
  }
  if (val.length < 3) return false;
  if (!validHdrChars[val.charCodeAt(2)]) {
    debug('invalid header, index 2, char "%s"', val.charCodeAt(2));
    return true;
  }
  if (val.length < 4) return false;
  if (!validHdrChars[val.charCodeAt(3)]) {
    debug('invalid header, index 3, char "%s"', val.charCodeAt(3));
    return true;
  }
  for (let i = 4; i < val.length; ++i) {
    if (!validHdrChars[val.charCodeAt(i)]) {
      debug('invalid header, index "%i", char "%s"', i, val.charCodeAt(i));
      return true;
    }
  }
  return false;
}
